1. Field of the Invention
The present invention relates to a response sensing device that senses response of an exhaust gas component concentration sensor, which senses a component concentration of exhaust gas of a diesel engine, for degradation determination of the exhaust gas component concentration sensor.
2. Description of Related Art
There is a device described in Patent document 1 (JP-A-2007-309103) known as a device that performs degradation determination of an exhaust gas component concentration sensor such as an oxygen concentration sensor provided in an exhaust system of an internal combustion engine.
The device described in Patent document 1 performs fuel cut for cutting fuel supply to the engine in order to perform the degradation determination of a response characteristic of the oxygen concentration sensor. The device calculates a reference estimation NG sensor output used for the degradation determination by using an output voltage of the oxygen concentration sensor at the time when the output voltage decreases from the output voltage as of start of the fuel cut operation by a predetermined voltage. It is determined that the oxygen concentration sensor has degraded if the actually sensed output of the oxygen concentration sensor indicates an air-fuel ratio richer than the reference estimation NG sensor output.
As mentioned above, for the degradation determination of the exhaust gas component concentration sensor in a gasoline engine, the fuel cut is performed to change a fuel injection quantity stepwise. Whether the response of the oxygen concentration sensor is good or bad is diagnosed based on the output change of the oxygen concentration sensor at the time.
However, it is not desirable to perform response diagnosis of an exhaust gas component concentration sensor such as an oxygen concentration sensor of a diesel engine by using a method similar to the method of the gasoline engine. It is because a rotation fluctuation or torque change occurs in the diesel engine immediately when the fuel injection quantity is changed stepwise in the diesel engine.
In order to solve such the problem, differently from the gasoline engine, an intake air quantity of the diesel engine may be changed and the response of the exhaust gas component concentration sensor of the diesel engine may be sensed from an output change of the exhaust gas component concentration sensor at the time.
However, when an intake actuator such as a throttle valve or an EGR valve is used as a means for changing the intake air quantity of the diesel engine, there is a possibility that a response time necessary for causing the change in the intake air quantity varies due to a variation among the individual intake actuators or aging degradation of the intake actuator.
Change in the response time, which is necessary for causing the change in the intake air quantity with the intake actuator, affects speed of occurrence of change in an exhaust gas component. Therefore, even when lowering of the response of the exhaust gas component concentration sensor is detected, it is quite difficult to distinguish whether the cause of the lowering is the change in the response time of the intake actuator or just the lowering of the response of the exhaust gas component concentration sensor.